Fine structure of theD2andF2sequences in Mgii investigated by level crossing and anticrossing spectroscopy

The fine-structure splittings of $\mathrm{nd}{}_{}{}^2{}_{}{}^{}D\mathrm{}(n=5-7\mathrm{})\mathrm{}$ and $\mathrm{nf}{}_{}{}^2{}_{}{}^{}F\mathrm{}(n=4-6\mathrm{})\mathrm{}$ levels in singly-ionized magnesium have been determined by means of fast-beam, level-crossing, and anticrossing spectroscopy. The inverted ${}_{}{}^2{}_{}{}^{}D$ fine-structure splittings are found to be approximately 8% smaller than predicted by recent theoretical calculations based upon many-body theory. The ${}_{}{}^2{}_{}{}^{}F$ fine-structure splittings are found to be approximately 3%-7% smaller than the theoretical values for the corresponding hydrogenic levels.